Alumina-based sintered material

Abstract

A homogeneous alumina-based sintered material having excellent grindability, low porosity and high flexural strength, and which is free of color unevenness and fluctuations in density. Predetermined amounts of Al 2 O 3 powder, MgO powder, CaCO 3 powder and SiO 2 powder are measured out, and then mixed with stirring in a ball mill. The mixture is granulated using a spray dryer, and then hydrostatically pressed to obtain a molded product having a predetermined shape. Subsequently, the molded product is stored and sintered at a temperature of 1,550° C. to 1,650° C., particularly 1,600° C. to 1,650° C. under atmospheric pressure for 2 hours. As a result, an alumina-based sintered material having a 50 percent cumulative grain size distribution in diameter of from 4 to 15 μm, a 90 percent grain diameter of two to three times the 50 percent grain diameter, and a porosity of not more than 5% can be obtained. The alumina-based sintered material thus obtained exhibits a maximum load current during grinding of not more than 1.0 A/mm, particularly not more than 0.5 A/mm, and a four-point flexural strength of not less than 300 MPa, thus providing excellent grindability as well as high strength.

What is claimed is: 
     
       1. A sintered material comprising MgO in an amount of from greater than 0 to 1% by weight, CaO in an amount of from 0.02 to 1% by weight, SiO 2  in an amount of from 0.02 to 0.8% by weight and Al 2  O 3  in an amount of at least 98% by weight, having a SiO 2  content ratio of less than 80 parts by weight based on 100 parts by weight of the sum of the weight of MgO, CaO and SiO 2 , a 50 percent cumulative grain size distribution in diameter of from 4 to 15 μm, a 90 percent diameter of not more than three times the 50 percent diameter, and a porosity of 2% or less. 
     
     
       2. The sintered material as claimed in claim 1, wherein the sintered material is grindable and a maximum load current measured during grinding is not more than 1.0 A/mm, when the maximum load current during grinding is measured using a surface grinding machine having a wheel motor, a voltage of 220 V is applied to the wheel motor which is connected to an ammeter, the load current developed during grinding is measured under the following conditions, and the load current is obtained by dividing the measured current by the width of the wheel: Grinding machine: precision surface grinding machine;   Grinding method: creep feed surface grinding;   Wheel: resin bond diamond wheel (grain size: #170, outer periphery: 205 mm, wheel width: 10 mm);   Number of wheel revolutions: 3,600 rpm;   Table feed rate: 60 mm/min;   Depth of cut: 3 mm/pass; and   Grinding distance: 30 mm.   
     
     
       3. A sintered material comprising MgO in an amount of from greater than 0 to 0.4% by weight, CaO in an amount of from 0.02 to 0.7% by weight, SiO 2  in an amount of from 0.02 to 0.8% by weight, and Al 2  O 3  in an amount of at least 98% by weight, having a SiO 2  content ratio of less than 80 parts by weight based on 100 parts by weight of the sum of the weight of MgO, CaO and SiO 2 , a 50 percent cumulative grain size distribution in diameter of from 6 to 12 μM, a 90 percent diameter of not more than three times the 50 percent diameter, a porosity of 2% or less, and a four-point flexural strength of not less than 300 MPa. 
     
     
       4. The sintered material as claimed in claim 3, wherein the sintered material is grindable and a maximum load current measured during grinding of not more than 0.5 A/mm, when the maximum load current during grinding is measured using a surface grinding machine having a wheel motor, a voltage of 220 V is applied to the wheel motor which is connected to an ammeter, the load current developed during grinding is measured under the following conditions, and the load current is obtained by dividing the measured current by the width of the wheel: Grinding machine: precision surface grinding machine;   Grinding method: creep feed surface grinding;   Wheel: resin bond diamond wheel (grain size: #170, outer periphery: 205 mm, wheel width: 10 mm);   Number of wheel revolutions: 3,600 rpm;   Table feed rate: 60 mm/min;   Depth of cut: 3 mm/pass; and   Grinding distance: 30 mm.   
     
     
       5. The sintered material as claimed in claim 1, comprising Al 2  O 3  in an amount of not less than 99.3% by weight. 
     
     
       6. The sintered material as claimed in claim 3, comprising Al 2  O 3  in an amount of not less than 99.3% by weight. 
     
     
       7. The sintered material as claimed in claim 2, which exhibits a maximum load current during grinding of not more than 0.3 A/mm and a four-point flexural strength of not less than 320 Mpa. 
     
     
       8. The sintered material as claimed in claim 4, which exhibits a maximum load current during grinding of not more than 0.3 A/mm and a four-point flexural strength of not less than 320 Mpa. 
     
     
       9. The sintered material as claimed in claim 5, which exhibits a maximum load current during grinding of not more than 0.3 A/mm and a four-point flexural strength of not less than 320 Mpa. 
     
     
       10. The sintered material as claimed in claim 3, wherein the 50 percent cumulative grain size distribution in diameter is from 6 to 10 μm and the 90 percent diameter is from two to three times the 50 percent diameter. 
     
     
       11. A sintered material consisting essentially of MgO in an amount of from greater than 0 to 1% by weight, CaO in an amount of from 0.02 to 1% by weight, SiO 2  in an amount of from 0.02 to 0.8% by weight and Al 2  O 3  in an amount of at least 98% by weight, having a SiO 2  content ratio of less than 80 parts by weight based on 100 parts by weight of the sum of the weight of MgO, CaO and SiO 2 , a 50 percent cumulative grain size distribution in diameter of from 4 to 15 μm, a 90 percent diameter of not more than three times the 50 percent diameter, and a porosity of 3% or less. 
     
     
       12. The sintered material as claimed in claim 11, wherein the sintered material is grindable and a maximum load current measured during grinding is not more than 1.0 A/mm, when the maximum load current during grinding is measured using a surface grinding machine having a wheel motor, a voltage of 220 V is applied to the wheel motor which is connected to an ammeter, the load current developed during grinding is measured under the following conditions, and the load current is obtained by dividing the measured current by the width of the wheel: Grinding machine: precision surface grinding machine;   Grinding method: creep feed surface grinding;   Wheel: resin bond diamond wheel (grain size: #170, outer periphery: 205 mm, wheel width: 10 mm);   Number of wheel revolutions: 3,600 rpm;   Table feed rate: 60 mm/min;   Depth of cut: 3 mm/pass; and   Grinding distance: 30 mm.   
     
     
       13. A sintered material consisting essentially of MgO in an amount of from greater than 0 to 0.4% by weight, CaO in an amount of from 0.02 to 0.7% by weight, SiO 2  in an amount of from 0.02 to 0.8% by weight and Al 2  O 3  in an amount of at least 98% by weight, having a SiO 2  content ratio of less than 80 parts by weight based on 100 parts by weight of the sum of the weight of MgO, CaO and SiO 2 , a 50 percent cumulative grain size distribution in diameter of from 6 to 12 μm, a 90 percent diameter of not more than three times the 50 percent diameter, a porosity of not more than 3%, and a four-point flexural strength of not less than 300 MPa. 
     
     
       14. The sintered material as claimed in claim 13, wherein the sintered material is grindable and a maximum load current measured during grinding of not more than 0.5 A/mm, when the maximum load current during grinding is measured using a surface grinding machine having a wheel motor, a voltage of 220 V is applied to the wheel motor which is connected to an ammeter, the load current developed during grinding is measured under the following conditions, and the load current is obtained by dividing the measured current by the width of the wheel: Grinding machine: precision surface grinding machine;   Grinding method: creep feed surface grinding;   Wheel: resin bond diamond wheel (grain size: #170, outer periphery: 205 mm, wheel width: 10 mm);   Number of wheel revolutions: 3,600 rpm;   Table feed rate: 60 mm/min;   Depth of cut: 3 mm/pass; and   Grinding distance: 30 mm.   
     
     
       15. The sintered material as claimed in claim 11, wherein the Al 2  O 3  is in an amount of not less than 99.3% by weight. 
     
     
       16. The sintered material claimed in claim 13, wherein the Al 2  O 3  is in an amount of not less than 99.3% by weight. 
     
     
       17. The sintered material as claimed in claim 12, which exhibits a maximum load current during grinding of not more than 0.3 A/mm and a four-point flexural strength of not less than 320 Mpa. 
     
     
       18. The sintered material as claimed in claim 14, which exhibits a maximum load current during grinding of not more than 0.3 A/mm and a four-point flexural strength of not less than 320 Mpa. 
     
     
       19. The sintered material as claimed in claim 15, which exhibits a maximum load current during grinding of not more than 0.3 A/mm and a four-point flexural strength of not less than 320 Mpa. 
     
     
       20. The sintered material as claimed in claim 13, wherein the 50 percent cumulative grain size distribution in diameter is from 6 to 10 μm and the 90 percent diameter is from two to three times the 50 percent diameter.